Answer:
-32.3 kJ
Explanation:
Step 1: Write the balanced thermochemical equation
2 Na₂O₂(s) + 2 H₂O(l) ⇒ 4 NaOH(s) + O₂(g) ΔH° = -126 kJ
Step 2: Calculate the moles corresponding to 40.0 g of Na₂O₂
The molar mass of Na₂O₂ is 77.98 g/mol.
40.0 g × 1 mol/77.98 g = 0.513 mol
Step 3: Calculate the amount of heat released upon the reaction of 0.513 moles of Na₂O₂
According to the thermochemical equation, 126 kJ of heat are released every 2 moles of Na₂O₂.
0.513 mol Na₂O₂ × (-126 kJ/2 mol Na₂O₂) = -32.3 kJ
